Recording and reproduction of sound



Dec. 20, 1932. J MAUREYR JR 1,891,388

RECORDING AND REPRODUCTION OF SOUND Filed Oct. 28, 1931 2 Sheets-Sheet l INVENTOR v JOHN A. MAURER JR.

BY M6 0- ATTORNEY I Dec. 20, MAURER, JR 1,891,388

RECORDING AND REPRODUCTION OF SOUND Filed Oct. 28, 1931 2 Sheets-Sheet '2 INVENTOR JOHN A. MAURER JR.

. BY I ATTORNEY Patented Dec. 20. 1932 JOHN A. MAUREB, JR,

OF NEW YORK, N. Y., ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE RECORDING AND REPRODUCTION OF SOUND Application filed October 28, 1931. Serial No. 571,533.

This invention relates to the recording and reproduction of sound, and has for its principal object the provision of an improved method and apparatus whereby relative movement between a record and a sound recording or sound reproducing element may be very accurately controlled.

In order to facilitate an understanding of the invention it will be described as utilized in the recording of sound on a photographic film along a helical path or track, and in the reproduction of sound from such a record. Specifically the application is to the type of record hereinafter referred to as microphotographic, that is, 'a. record wherein the sound track is of the order of a few thousandths of an inch wide. In one successfully operated embodiment of the invention the width of the helical sound track is two thousandths of an inch and the spacing from center to center of adjacent tracks is four thousandths. It should be understood that these specific dimensions are given only for purposes 0 illustration, and that the invention is in no wise limited to them.

In reproducing sound from such a record a beam of light in the form of a rectangle of length nearly equal to the width of the sound track is made to pass through the film while the latter is moved at a constant speed.

It will be readily apparent that if this light beam is not at all times accurately registered upon the track the sound reproduction will be distorted.

This invention is in some respects an improvement on the invention disclosed by a Patent 1,77 6,123, granted to J. C. Kroesen on September 16, 1930. This patent discloses in Fig.1 a helical type sound record provided with sprocket holes; in Figs. 2 and 3 a sound reproducer wherein the light source and photo cell are moved transversely of a sprocket driven film, and in Fig. 4 a sound reproducer wherein the sprocket driven film is moved relatively to light source and photo cell, in each casein such a way that the light beam follows the displacement of the helical track across the width of the film. 5

The recording of sound in the form of a helical record and the reproduction of sound vance' the light from such a record by the sprocket drive mechanism disclosed in the aforesaid patent, however, is not altogether satisfactory from a practical viewpoint for the reason that the registry of the light beam on the sound track ifis1 likely to be disturbed by shrinkage of the m. Thus in using the mechanism disclosed in the Kroesen patent the film loop is driven by the sprocket a constant number of revolutions per unit time or a constant number of sprocket holes per unit time, while at the same time the gear train and lead screw adsource and photocell a definit e distance. If this distance is chosen to be correct for unshrunken film there will be a variable amount of inaccuracy in the registration on shrunken films. Since in practice shrinkage of the developed record may amount to any value up to about one and onehalf percent, it is not possible to compensate for it by -a particular choice of the rate of feed of the lead screw. Shrinkage of negative stock is of the order of one-tenth to onefourth of one percent and likewise varies 7 in different 'cases.

This lack of registration due to film shrinkage becomes more serious as the sound track is made narrower, and in the case of a track of the microscopic dimensions referred to above it may amount to several times the width of the track.

It is possible to introduce compensating means whereby the rate of advance of the light beam is varied to correspond with the shrinkage of the film, thereby maintaining correct registry with sprocket drive of the film. Such means are to form the subject matter ofa subsequent application.

In accordance with the present invention, however, this lack of registry; between the beam and track is obviated 'by driving the film through frictional contact. Thus if the record is made with a constant lateral displacement of the helical track and is driven by close frictional engagement with a wheel or drum driven at uniform s eed, it will be I moved a constant number 0 feet per-l'unit time. Under these conditions, the displacement of the v.record per unit length of the film will be the same on the shrunken film as on the unshrunken film and the light beam will follow the record accurately regardless of shrinkage. The only result of shrinkage will be that the pitch of the reproduced sound is raised slightly. This rise in pitch has been unobjectionable from a practical viewpoint.

Since the film must be guided laterally by its edge, there will be a slight displacement of the initial record turn relative to the light beam due to shrinkage. This error however results only from shrinkage in the relatively narrow marginal area and may be corrected by making the starting point of the beams correspond to a partly shrunken film and allowing the beam to overlap the sound track, thus permitting slight variation in shrinkage without seriously disturbing the registry between the beam and track. In the practical use of the apparatus, it has been found satisfactory to place the shrunken film on its support and adjust the position of the light beam so that it registers with the first turn of the track.

The invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings:

Figure 1 illustrates an unshrunken loop of lm bearing a helical sound record,

Figure 2 illustrates the same loop of film after shrinkage has taken place, and

igure 3 illustrates a form of frictional drive mechanism whereby this record may be recorded and reproduced.

In Figures 1 and 2 only one turn of the helix is shown for the sake of clearness and the shrinkage is shown greatly exaggerated. In practice the helix may consist of as many as three hundred turns, and the shrinkage may be of the order of one percent.

In the recording of the sound track shown in Figure 1 the light beam starts at 1 and advances laterally at the same time that the loop is moved lengthwise, so that at the end of a certain time the light has reached the position shown at 2. In reproducing from the same record if unshrunkenthe same action would take place. Shrinkage always takes place in processing, however, so that this condition does not exist in practice.

Now referring to Figure 2, if the film is driven by friction, in accordance with the present invention, at the end of the time referred to above the film will have been moved the same distance as before and the light beam which wasfirst registered at 1 will be passing through the point 2. Since the shrinkage of the film is the same laterally as longitudinally (a fact which has been established by experience) the rate of lateral displacement of the track is the same on he shrunken film, and if the light beam has been advanced at the same rate as before it will be in register with the track as shown at 2.

But if the film is driven by a sprocket it will have travelled a shorter distance in this period of time, because the pitch of the sprocket holes has been shortened, and the light beam will be at 3. Having been advanced too fast it will be out of register with the track, as shown. As is shown in the drawings, in the case of the sprocket drive the light beam will have scanned in any interval of time the same portion of the sound track which was recorded in the same interval of time, that is, the sounds are reproduced at their original pitch. They eventually become distorted, however, because of the inaccurate registry of the light beam.

When the film is driven by friction the light beam scans a greater portion of the sound record thanwas recorded in the same length of time, that is, the pitch of the sounds is slightly raised due to shrinkage of the film. In practlce this rise does not exceed one and one-half percent, and is entirely unobjectionable.

Figure 3 illustrates an apparatus wherein a light beam is moved by an optical system 10 across a record strip 11. It will be noted that the film 11 is driven by friction between it and a roller 12 mounted on a drive shaft 13; that the optical system 10 is coupled to the drive shaft 13 through gears 14 and 15, a lead screw 16 and a nut 17 which is connected to the optical system 10 through a support member 18 and is arranged to cooperate with the lead screw 16; and that a roller 19 pivoted at the point 20 and biased into contact with the film 11 by a spring 21 may be provided for ensuring proper contact between the film and the frictional drive roller 12.

It will be readily understood that the invention is useful in both the recording and reproduction of records, the illustrated apparatus being merely illustrative of one of its many possible forms. Thus if the apparatus is to be utilized as a recorder, the casing 22 at the left hand end may contain any suitable light modulating means such as a glow tube or light valve. If the apparatus is to be utilized as a producer, this casing may contain an exciter lamp of any suitable type. Also various modifications may obviously be made in the other features of theapparatus without departing from the spirit and scope of the invention which relates primarily to record driving means whereby the inaccuracies heretofore resulting from film shrinkage are obviated.

The invention disclosed to be generic and not use of the apparatus. to a sound recorder is application Serial No herein is believed limited to any specific Its specific application covered in a copending 571,532, filed October same assignee as 28, 1931, and its application to a sound reproducer is covered in a copending application, Serial No. 571,534, filed October 28, 1931, both these applications being assigned to the the present application. Having thus described my invention, what I claim is:

1. In an apparatus for producing relative movement between a record strip and a light beam, the combination of frictional drive means for moving said strip. at a substantially uniform linear speed, and means for mov-- ing said beam across said strip at a rate of speed proportional to said linear speed.

2. The method of producing relative movement between a record strip and a light beam which includes frictionally moving said strip at a substantially uniform linear speed, and moving said beam across said strip at a rate of speed proportional to said linear speed.

3. In an apparatus for producing relative movement between a continuous loop record and a light beam, the combination of frictional drive means for moving said loop at a substantially uniform linear speed, and

and means for moving said beam transversely of said strip at a speed proportional to the,

sions of said loop.

HN A. MAURER, JR.

means for moving said beam across said loop at a rate of speed proportional to said linear speed.

4. In an apparatus for movement between a record strip and a light beam, the combination of drive means for moving said beam across said film at a substantially uniform linear speed, and means operable in response to said drive means to move said film through frictional engagement at a rate of speed proportional to said linear speed.

5. The method of producing relative movestantially uniform linear speed, and moving said strip at a rate of speed which does not vary with respect to said linear speed irrespective of change in the dimensions of said strip.

6. The method of producing relative movement between a continuous loop record and a light beam which includes moving said beam at a substantially uniform linear s cod and moving said loop at a rate of speed w ich does not vary with respect to said linear speed irrespective of change in the dimensions of said record.

7. In an apparatus for producing relative movement between a strip bearing a record and a light beam, the combination of means for moving said strip longitudinally, and means for moving said beam transversel of said strip at a speed proportional to the width.

of saidrecord irrespective of shrinkage 0'3" said strip.

8. In an apparatus for producing relative movement between a light beam and a strip bearing sound record, the combination of means for moving said strip longitudinally,

producing relative ment between a record strip and a light beam 4 which includes. moving said beam at a sub- 

